Soluble coffee powder is a phrase used to describe coffee powder which has been prepared by extraction of roast and ground coffee followed typically by drying of the extract into a powdered product by conventional means such as freeze-drying, spray-drying or the like. In order to prepare a coffee beverage, hot water is then simply added to the powder thus avoiding the complicated and time-consuming process which is involved when preparing a beverage from traditional roast and ground coffee.
However, unlike coffee beverages prepared directly from roast and ground coffee, those prepared from instant soluble coffee do not usually exhibit a fine foam on their upper surface when reconstituted with hot water. The foamed upper surface in beverages prepared directly from roast and ground coffee are typically associated with and caused, at least in part, by the machines which brew with pressurised water and/or steam. This foam, also called “crema” is known to positively affect the mouthfeel of the product when consumed and so is highly desired by many consumers. Furthermore, the foam acts to keep more of the volatile aromas within the beverage so that they can be appreciated by the consumer rather than lost to the surrounding environment. If a similar foam is to be achieved in a coffee beverage prepared from soluble coffee powder, the foam must be generated by simple admixing of the soluble coffee powder and a liquid.
EP 2194795 and EP 0839457 discloses methods whereby gas is injected into a coffee extract which is subsequently spray dried to produce a spray dried soluble coffee powder producing foam when dissolved in a liquid. Freeze dried soluble coffee powders may have advantages over spray dried powders in terms of e.g. aroma and freeze dried powders are often perceived by consumers as being of superior quality, therefore there is a need to provide freeze dried powders which can produce foam upon dissolution. WO 2009/059938 and WO 2009/080596 disclose sintering methods for producing soluble coffee powders with a freeze dried or agglomerated texture and appearance which produces foam upon dissolution in a liquid. Sintering methods, however, are complex and cannot readily be implemented into existing facilities for producing freeze dried coffee. There is thus a need for simple methods to produce freeze dried coffee powders that produce a foam upon dissolution in a liquid.